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...ed together with the reduced electromagnetic interference (EMI) [18]. Moreover, the multilevel converters have the lowest demands for the input filters or alternatively reduced number of commutations =-=[19]-=-. For the same harmonic performance as a two-level converter, the switching frequency of a multilevel converter can be reduced to 25% that results in the reduction of the switching losses [20]. Even t...

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...industry has sustained the continuous development of multilevel converters due to their capability of handling voltages up to 6.9 kV and power of several megawatts [1]–[3]. Among different topologies =-=[4]-=-, the cascaded multicell [5], [6] inverter has received much attention. The original converter proposed in [5] and [6] uses cells with diode rectifiers that does not allow a transfer of power from the...

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...gns through analysis, simulation, and experiments. Index Terms—Capacitor voltage balance, diode-clamped, multilevel, pulsewidth modulation (PWM), virtual vector. I. INTRODUCTION MULTILEVEL converters =-=[1]-=-–[4] have opened the doorfor advances in electric energy conversion technology. These converters present the advantages of a lower device voltage rating, lower harmonic distortion, and higher efficien...

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...s[19].sWith the basic MLI topologies, the number of inverter levelssis linearly proportional to the number of inverter’s switchingsdevices and this limits the practical number of levels to fewslevels =-=[17]-=-. Inverter with extended number of levels havesbeen built using the asymmetrical MLI structure, where thesinverter’s cascaded H-bridges have been supplied withsdifferent voltage levels [9,10]. Asymmet...

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...d [8]. With the basic MLI topologies, the number of inverter levels is linearly proportional to the number of inverter’s switching devices and this limits the practical number of levels to few levels =-=[9]-=-. Inverter with extended number of levels have been built using the asymmetrical MLI structure, where the inverter’s Manuscript received October 09, 2011; revised February 05, 2012; accepted September...

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...of the flying capacitors can be chosen depending on the maximum voltage stress across them, permissible voltage variations across these capacitors and the maximum current flowing through each of them =-=[4]-=-, [9], [11]. Here, for simplicity, equal size of the capacitors are taken as , for each phase. The other parameters of the inverter are listed in Table III. With reference to Fig. 2, , and are chosen ...

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...ered that they are less reliable [1]. However, a different approach is to consider that medium voltage inverters offer more possibilities in the power circuit to allow for operation even during faulty conditions. This approach has recently been considered for the flying capacitor topology [2], [3], [4]. The design of a sensor to improve the short circuit tolerance of this topology is reported in [4]. This work is dedicated to a different family of medium voltage inverters, the so called cascaded multicell topology, which uses several cells in series connection to generate higher voltages [5], [6]. Each cell is supplied by an isolated three-phase secondary of the input transformer. This paper proposes a method to increase the reliability of cascaded multicell inverters, permitting the operation even with some faulty cells. This is achieved by adding small contactors in the power circuit and modifying the modulation strategy, to maintain the generation of balanced voltages. II. THE MEDIUM VOLTAGE INVERTER A. Power circuit Fig. 1 represents the power circuit of an 11-level medium voltage inverter, which has 5 cells in series connection in each phase. This inverter has 15 modules (cells)....